Field of the Invention
The invention relates to a display, and particular relates to a head-mounted display.
Description of Related Art
Near eye displays (NED) or head-mounted displays (HMD) are currently considered to be wearable displays that are full of potential. The NEDs are divided into the augmented reality (AR)-type and virtual reality (VR)-type based on whether an image of the surroundings can also be seen in actual use. Virtual reality emphasizes the sense of reality in a virtual world, namely a wide field of view that exceeds the extreme of human eyes. Augmented reality, on the other hand, focuses on providing the best image quality under the premise of making an apparatus more light-weighted. Currently, the key to the development of optical technologies for AR-type head-mounted displays is how the crucial requirements, namely field of view (FOV), size, weight, and appearance, can be taken into consideration at the same time.
In the conventional head-mounted display, an illumination beam modulated to meet the needs of an image output element is output from a light source module. After passing through the image output element, the illumination beam becomes a beam carrying image information (i.e., an image beam). Afterwards, the image beam passes through one or more lens elements and/or a mirror element and an imaging element and then is emitted to a projection target, such as the user's eye. Then, the crystalline lens of the eye focuses the image beam on the retina to form an image. Generally speaking, a projection area (in a circular shape, for example) of the image beam projected to the projection target is a circular area with a diameter from about 1.6 micrometers to about 2.0 micrometers. Therefore, the user's pupil must be located precisely on the position where the image beam is projected, so as to clearly see the virtual image. However, since the users' facial features may not be the same, an adjustment device must be additionally disposed, such that the position where the image beam is projected can be precisely located at the pupil positions of different users. In addition, in the conventional head-mounted display using an optical waveguide element, two beam splitter arrays are required to expand the lengths of the projection area of the image beam in two different directions (i.e., vertical and horizontal directions), making the size of the head-mounted display larger and cost of the head-mounted display higher.
The information disclosed in this “Description of Related Art” section is only for enhancement understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Furthermore, the information disclosed in this “Description of Related Art” section does not mean that one or more problems to be solved by one or more embodiments of the invention were acknowledged by a person of ordinary skill in the art.